277 research outputs found
Instanton Number Calculus on Noncommutative R^4
In noncommutative spaces, it is unknown whether the Pontrjagin class gives
integer, as well as, the relation between the instanton number and Pontrjagin
class is not clear. Here we define ``Instanton number'' by the size of
in the ADHM construction. We show the analytical derivation of the
noncommuatative U(1) instanton number as an integral of Pontrjagin class
(instanton charge) with the Fock space representation. Our approach is for the
arbitrary converge noncommutative U(1) instanton solution, and is based on the
anti-self-dual (ASD) equation itself. We give the Stokes' theorem for the
number operator representation. The Stokes' theorem on the noncommutative space
shows that instanton charge is given by some boundary sum. Using the ASD
conditions, we conclude that the instanton charge is equivalent to the
instanton number.Comment: 29 pages, 7 figures, some statements in Sec.4.3 correcte
Instanton calculus in R-R background and the topological string
We study a system of fractional D3 and D(-1) branes in a Ramond-Ramond closed
string background and show that it describes the gauge instantons of N=2 super
Yang-Mills theory and their interactions with the graviphoton of N=2
supergravity. In particular, we analyze the instanton moduli space using string
theory methods and compute the prepotential of the effective gauge theory
exploiting the localization methods of the instanton calculus showing that this
leads to the same information given by the topological string. We also comment
on the relation between our approach and the so-called Omega-background.Comment: 38 pages, 2 figures, JHEP class (included); final version to be
pubished in JHE
Compilation and critical review of GMPEs for the GEM-PEER Global GMPEs Project
International audienceGround-motion prediction equations (GMPEs) relate a ground-motion parameter (e.g. peak ground acceleration, PGA) to a set of explanatory variables describing the source, wave propagation path and site conditions. In the past five decades many hundreds of GMPEs for the prediction of PGA and linear elastic response spectral ordinates have been published. We discuss the pre-selection of GMPEs undertaken within the framework of the GEM-PEER Global GMPEs Project. The pre-selection criteria adopted were consistent with the current state-of-the-art in ground-motion characterization and sought to retain only the most robust GMPEs. Consideration of broad tectonic regionalization (e.g. shallow crustal seismicity in tectonically-active areas, stable continental regions and subduction zones) was made but it was assumed (based on previous studies) that strong regional differences were not present within these tectonic classes. In total about thirty GMPEs were pre-selected for closer inspection and testing to obtain a final set of ground-motion models
Instanton Number of Noncommutative U(n) gauge theory
We show that the integral of the first Pontrjagin class is given by an
integer and it is identified with instanton number of the U(n) gauge theory on
noncommutative . Here the dimension of the vector space that
appear in the ADHM construction is called Instanton number. The calculation is
done in operator formalism and the first Pontrjagin class is defined by
converge series. The origin of the instanton number is investigated closely,
too.Comment: 6 color figures, 27 pages, some comments and references are
added,typos fixe
Non-extremal fractional branes
We construct non-extremal fractional D-brane solutions of type-II string
theory at the Z_2 orbifold point of K3. These solutions generalize known
extremal fractional-brane solutions and provide further insights into N=2
supersymmetric gauge theories and dual descriptions thereof. In particular, we
find that for these solutions the horizon radius cannot exceed the non-extremal
enhancon radius. As a consequence, we conclude that a system of non-extremal
fractional branes cannot develop into a black brane. This conclusion is in
agreement with known dual descriptions of the system.Comment: 29 pages, LaTeX. v2: 30 pages; equation (3.4) corrected; typos fixed;
discussion in section 3 streamlined and slightly extended; reference adde
Quasi-localized states on noncommutative solitons
We consider noncommutative gauge theories which have zero mass states
propagating along both commutative and noncommutative dimensions. Solitons in
these theories generically carry U(m) gauge group on their world-volume. From
the point of view of string theory, these solitons correspond to
``branes within branes''. We show that once the world-volume U(m) gauge
theory is in the Higgs phase, light states become quasi-localized, rather than
strictly localized on the soliton, i.e. they mix with light bulk modes and have
finite widths to escape into the noncommutative dimensions. At small values of
U(m) symmetry breaking parameters, these widths are small compared to the
corresponding masses. Explicit examples considered are adjoint scalar field in
the background of a noncommutative vortex in U(1)-Higgs theory, and gauge
fields in instanton backgrounds in pure gauge noncommutative theories.Comment: 27 pages, references and comments added, final version to appear in
JHE
Instantons on Quivers and Orientifolds
We compute the prepotential for gauge theories descending from
SYM via quiver projections and mass deformations.
This accounts for gauge theories with product gauge groups and bifundamental
matter. The case of massive orientifold gauge theories with gauge group SO/Sp
is also described. In the case with no gravitational corrections the results
are shown to be in agreement with Seiberg-Witten analysis and previous results
in the literature.Comment: 28 pages, revised version, references added, some typos correcte
Perspectives on safety culture
Overviewing selected elements from the literature, this paper locates the notion of safety culture within its parent concept of organisational culture. A distinction is drawn between functionalist and interpretive perspectives on organisational culture. The terms ‘culture’ and ‘climate’ are clarified as they are typically applied to organisations and to safety. A contrast is drawn between strategic top down and data-driven bottom up approaches to human factors as an illustrative aspect of safety. A safety case study is used to illustrate two measurement approaches. Key issues for future study include valid measurement of safety culture and developing methods to adequately represent mechanisms through which safety culture might influence, and be influenced by, other safety factors
Fusion of secretory vesicles isolated from rat liver
Secretory vesicles isolated from rat liver were found to fuse after exposure to Ca2+. Vescle fusion is characterized by the occurrence of twinned vesicles with a continuous cleavage plane between two vesicles in freeze-fracture electron microscopy. The number of fused vesicles increases with increasing Ca2+-concentrations and is half maximal around 10–6 m. Other divalent cations (Ba2+, Sr2+, and Mg2+) were ineffective. Mg2+ inhibits Ca2+-induced fusion. Therefore, the fusion of secretory vesiclesin vitro is Ca2+ specific and exhibits properties similar to the exocytotic process of various secretory cells.
Various substances affecting secretionin vivo (microtubular inhibitors, local anethetics, ionophores) were tested for their effect on membrane fusion in our system.
The fusion of isolated secretory vesicles from liver was found to differ from that of pure phospholipid membranes in its temperature dependence, in its much lower requirement for Ca2+, and in its Ca2+-specificity. Chemical and enzymatic modifications of the vesicle membrane indicate that glycoproteins may account for these differences
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